This invention relates to the production of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon. More particularly, the invention relates to a method of making novel catalyst compositions and a novel process for the production of such polymers employing the catalyst compositions in the process.
The invention relates to homogeneous catalysts for copolymerization of carbon monoxide and alpha olefins, methods for preparing these catalysts, and a process of copolymerizing alpha-olefins and carbon monoxide using these catalysts. More particularly, the invention relates to a homogeneous catalyst useful for making polymers containing carbon monoxide and olefins in interpolymerized form.
The process of producing linear alternating copolymers of carbon monoxide and ethylenically unsaturated compounds is described in U.S. Pat. No. 3,835,123 and U.S. Pat. No. 3,984,388. These polymers are represented by the general structural formula --A--B--A--B-- (where A=olefin and B=carbonyl). When the olefin is ethylene the resulting polymer may be represented by the formula ##STR1##
In the case where propylene is present in the reaction mixture, the polymer will have C.sub.3 units randomly scattered through the olefinic portion of the polymer. The C.sub.3 units do not interfere with or disrupt the linear alternating structure of the polymer in that only one olefinic unit is located between two carbonyl goups. ##STR2##
An improvement in the process of making carbon monoxide/.alpha.-olefin polymers was described in EPO applications 0 121 965 A2 and 0 181 014 A1. It was reported that more active catalysts resulted when the catalyst composition was based on Group VIII metals of the Mendeleev Periodic Table, an anion of a non-hydrohalogenated acid with a pKa of less than 2 and a bidentate ligand containing phosphorous, arsenic or antimony dentate groups which can complex with the metal. For example, Pd, Co or Ni are given as the transition metal sources with anions that could be used including hexafluorophosphate (PF.sub.6.sup.-), trichloroacetate and tetrafluoroborate (BF.sub.4.sup.-) which are respectively the conjugate anions of hexafluorophosphoric acid, trichloroacetic acid and tetrafluoroboric acid.
U.S. Pat. No. 4,804,739 describes the use of catalysts based on palladium as the transition metal source and quaternary phosphonium salts for the anion source. These catalysts reduce the amount of metallic residues in the product. The catalyst compositions generally consist of a palladium(II) salt (such as a halide or acetate), a strong organic acid (such as trifluoroacetic, p-toluenesulfonic acid) and a bidentate phosphine (such as, 1,3-bis[diphenylphosphino]propane).
U.S. Pat. No. 4,831,114 discloses the use of a catalyst containing a Group VIII metal, an anion of a non-hydrohalogenic acid having a pKa more than about 2 but less than 4, and certain bidentate hydrocarbyl phosphine ligands. The composition is described as exhibiting greater reactivity at lower reactor temperatures.
EPO application 0 396 268 A1 describes the use of a catalyst including a palladium(II) salt, a bidentate amine, phosphine, arsine or stibene and specified anions. Quinone was added as an oxidant to prevent reduction of the transition metal. Quinones are described as being useful in maintaining catalyst stability.
A different catalyst system for the polymerization of carbon monoxide and alpha olefins involves the use of cationic palladium (II) catalysts. Researchers have reported the use of a cationic palladium (II) compound [Pd(CH.sub.3 CN).sub.4 ].sup.+2 [(BF.sub.4)].sub.2.sup.- to polymerize styrene, .alpha.-methyl styrene, cyclohexene, norbornylene and norbornadiene under mild conditions. (Sen, Organometallics 1982, 1, 415-417). Cationic palladium (II) has been reported for ethylene/carbon monoxide polymerization using [bis(acetonitrile)palladium(II) 1,3-bis(diphenylphosphino)propane] [bis(tetrafluoroborate)] and [Pd(triphenylphosphine).sub.n (CH.sub.3 CN).sub.4-n ](BF.sub.4).sub.2 (where n=1-3). Advances in Polymer Science, 73/74, Springer-Verlag, New York, 1986 pages 126-44.
Processing and fabrication of articles from ethylene/carbon monoxide linear alternating copolymers produced by prior art processes and catalyst are difficult. The melting point of such copolymers is close to their thermal decomposition point, and this made thermal fabrication techniques difficult to control. This problem can be overcome by adding small amounts of propylene into the polymerization reaction mixture. The propylene is interpolymerized into the polymer backbone and decreases the melt point or temperature at which a reasonable melt flow will occur of the terpolymer product. U.S. Pat. Nos. 4,866,128 and 4,904,716 show that terpolymers prepared with a melting range of 220.degree. to 235.degree. C. are more useful for fabrication processes.
U.S. Pat. No. 4,866,128 teaches another approach for controlling the melting range of olefin/carbon monoxide polymers by blending them with other polymers. Only limited success has been achieved by this technique due to the apparent incompatibility of the ethylene/carbon monoxide copolymer with other materials, even under melt processing conditions. See, for example, U.S. Pat. Nos. 4,904,728 and 4,954,570.
A need exists for a more versatile catalyst which can incorporate a larger variety of olefinic comonomers into the polymer at high catalyst efficiency and higher reaction rates. Such a catalyst would provide flexibility in controlling the melt flow characteristics of this polymer and terpolymers by varying the olefinic component and would permit the preparation of polymers which range from completely amorphous to highly crystalline.
There is also a need for a catalyst composition which does not require the presence of a strong acid component. Such a catalyst would have significant advantages, e.g., lower corrosion rate of process equipment and lower toxicity.